2.5 Controlling What Gets Processed

Definition processing directives can only be processed
if the ’#’ character is the first character on a line. Also, if you
want a ’#’ as the first character of a line in one of your string
assignments, you should either escape it by preceding it with a
backslash ‘\’, or by embedding it in the string as in "\n#".

All of the normal C preprocessing directives are recognized, though
several are ignored. There is also an additional #shell -
#endshell pair. Another minor difference is that AutoGen
directives must have the hash character (#) in column 1.
Unrecognized directives produce an error.

The final tweak is that #! is treated as a comment line.
Using this feature, you can use: ‘#! /usr/local/bin/autogen’
as the first line of a definitions file, set the mode to executable
and "run" the definitions file as if it were a direct invocation of
AutoGen. This was done for its hack value.

The AutoGen recognized directives are:

#assert

This directive is processed, but only if the expression begins with
either a back quote (`) or an open parenthesis (().
Text within the back quotes are handed off to the shell for processing
and parenthesized text is handed off to Guile. Multiple line expressions
must be joined with backslashes.

If the shell-script or scheme-expr do not yield true
valued results, autogen will be aborted. If <anything else> or
nothing at all is provided, then this directive is ignored.

The result is false (and fails) if the result is empty, the
number zero, or a string that starts with the letters ’n’ or ’f’ ("no"
or "false").

#define

Will add the name to the define list as if it were a DEFINE program
argument. Its value will be the first non-whitespace token following
the name. Quotes are not processed.

After the definitions file has been processed, any remaining entries
in the define list will be added to the environment.

#elif

Marks a transition in the #if directive. Error when out of context.
#if blocks are always ignored.

#else

This must follow an #if, #ifdef or #ifndef.
If it follows the #if, then it will be ignored. Otherwise,
it will change the processing state to the reverse of what it was.

#endif

This must follow an #if, #ifdef or #ifndef.
In all cases, this will resume normal processing of text.

#endmac

Marks the end of the #macdef directive. Error when out of context.

#endshell

Marks the end of the #shell directive. Error when out of context.

#error

This directive will cause AutoGen to stop processing
and exit with a status of EXIT_FAILURE.

#ident

Ignored directive.

#if

#if expressions are not analyzed. Everything from here
to the matching #endif is skipped.

#ifdef

The definitions that follow, up to the matching #endif will be
processed only if there is a corresponding -Dname command line
option or if a #define of that name has been previously encountered.

#ifndef

The definitions that follow, up to the matching #endif will be
processed only if the named value has not been defined.

#include

This directive will insert definitions from another file into
the current collection. If the file name is adorned with
double quotes or angle brackets (as in a C program), then the
include is ignored.

#let

Ignored directive.

#line

Alters the current line number and/or file name. You may wish to
use this directive if you extract definition source from other files.
getdefs uses this mechanism so AutoGen will report the correct
file and approximate line number of any errors found in extracted
definitions.

#macdef

This is a new AT&T research preprocessing directive. Basically, it is
a multi-line #define that may include other preprocessing directives.
Text between this line and a #endmac directive are ignored.

#option

This directive will pass the option name and associated text to the
AutoOpts optionLoadLine routine (see section optionLoadLine). The
option text may span multiple lines by continuing them with a backslash.
The backslash/newline pair will be replaced with two space characters.
This directive may be used to set a search path for locating template files
For example, this:

#option templ-dirs $ENVVAR/dirname

will direct autogen to use the ENVVAR environment variable to find
a directory named dirname that (may) contain templates. Since these
directories are searched in most recently supplied first order, search
directories supplied in this way will be searched before any supplied on
the command line.

#pragma

Ignored directive.

#shell

Invokes $SHELL or ‘/bin/sh’ on a script that should
generate AutoGen definitions. It does this using the same server
process that handles the back-quoted ` text.
The block of text handed to the shell is terminated with
the #endshell directive.

CAUTION let not your $SHELL be csh.

#undef

Will remove any entries from the define list
that match the undef name pattern.